1. Field of the Invention
This invention relates to a metal-to-metal fluid tight seal configuration formed between two abutting threaded tubular members comprising a downhole member used in a subterranean oil and/or gas well.
2. Description of the Prior Art
In subterranean oil and/or gas wells fluid tight seals must be established between components used for the transmission of oil or gas from the producing formation to the surface of the well or for the injection of fluids into the well. The most common means of maintaining sealing integrity is to utilize polymeric seals between adjacent metallic members. Quite often these seals are of an elastomeric material and seals having a conventional O-ring configuration, a chevron configuration or a T-shaped configuration are often used in downhole assemblies. It is quite common to use an elastomeric O-ring seal to prevent leakage between two threaded tubular members or components. U.S. Pat. No. 2,980,451 discloses an extrudable member used to establish sealing integrity between two threaded members.
Another means of maintaining a metal-to-metal seal between tubular components is to employ a fluid tight threaded connection. These conventional fluid tight threaded connections are commonly referred to as a premium threaded connections and employ a special thread contour such that mating threads are always forming a stressed metal-to-metal circumferentially continuous seal. One well-known threaded premium connection is commonly referred to as the Hydril "CS" connection, which was developed by Hydril Company and is described in U.S. Pat. No. 3,100,656. Another such threaded connection is shown in U.S. Pat. No. 3,185,502. These premium threads are most often employed to establish an interconnection between abutting oil well pipe or tubing members to prevent leakage through the interconnected box and pin members.
Conventional use of premium threaded connections and of elastomeric O-ring seals to form a fluid tight connection between box and pin members does, however, necessitate certain compromises. The wall thickness for abutting box and pin tubular members will of necessity be greater when these prior art fluid tight connections are employed than when a conventional non-sealing threaded profile is used. This invention overcomes these dimensional limitations by employing a separate plastically deformable metallic ring to establish the metal-to-metal seal during rotational engagement but independent of the profile of conventional threaded connections.
Plastically deformed circular rings have been used to form a seal between members employed for the transmission of oil and/or gas. One example is the use of a circular ring or ring-joint gasket to form a metal-to-metal seal for flanged wellheads. These flanged wellheads can be constructed according to publications of the American Petroleum Institute including the API Specification for Wellhead Equipment, API Spec. 6A, Thirteenth Edition, 1981. These flanged wellheads employ a circular metallic ring trapped in a groove on one of two mating members. These API flanged wellheads are assembled by bolting the two mating non-rotating members together. During mating the metallic rings are plastically deformed to some extent and engage both of the mating members, but there is no relative rotation between mating members.